Single crystal SiC and a method of producing the same

ABSTRACT

A complex (M) which is formed by growing a polycrystalline β-SiC plate 4 by the thermal CVD method on crystal orientation faces which are unified in one direction of plural plate-like single crystal α-SiC pieces 2 that are stacked and closely contacted is subjected to a heat treatment at a temperature in the range of 1,850 to 2,400° C., whereby a single crystal which is oriented in the same direction as the crystal axes of the single crystal α-SiC pieces 2 is grown from the crystal orientation faces of the single crystal α-SiC pieces toward the polycrystalline β-SiC plate 4. As a result, single crystal SiC of a high quality in which crystalline nuclei, impurities, micropipe defects, and the like are not substantially generated in an interface can be produced easily and efficiently.

TECHNICAL FIELD

The present invention relates to single crystal SiC and a method ofproducing the same, and more particularly to single crystal SiC which isused as a semiconductor substrate wafer for a light-emitting diode, anX-ray optical element such as a monochrometer, a high-temperaturesemiconductor electronic element, a power device, or the like, and alsoto a method of producing the same.

BACKGROUND ART

SiC (silicon carbide) is superior in heat resistance and mechanicalstrength than an existing semiconductor material such as Si (silicon)and GaAs (gallium arsenide), and also has good high-temperatureproperties, high-frequency properties, dielectric strength, andresistance to environments. In addition, it is easy to perform thevalence control of electrons and holes by doping an impurity. Moreover,SiC has a wide band gap (for example, single crystal 6H-SiC has a bandgap of about 3.0 eV, and single crystal 4H-SiC has a band gap of 3.26eV). For these reasons, single crystal SiC receives attention and isexpected as a semiconductor material for a next-generation semiconductormaterial for a power device.

As a method of producing (growing) single crystal SiC of this type,conventionally, known are the Achison method which is generally known asan industrial method of producing an SiC abrasive material, and thesublimation and recrystallization method in which powder SiC produced bythe Achison method is used as a raw material and a crystal is grown on asingle crystalline nucleus.

In the Achison method of the above-described conventional productionmethods, however, a single crystal is grown slowly over a long timeperiod, so that the crystal growth rate is very low. In addition, alarge number of crystalline nuclei are generated in an initial growthstage, and they propagate to an upper portion of the crystal as thecrystal growth advances. Thus, it is difficult to singly obtain alarge-size single crystal.

In the sublimation and recrystallization method, a high-speed growth ofabout 1 mm/hr. is adopted mainly for an economical reason (productioncost), so that impurities and pin holes which have a diameter of severalmicrons and which pass through the crystal in the growing direction arelikely to remain in a growing crystal. Such pin holes are calledmicropipe defects and cause a leakage current when a semiconductordevice is fabricated. Accordingly, there exists a problem in that singlecrystal SiC having a sufficiently good quality cannot be obtained. Thisblocks a practical use of SiC which has many superior characteristics ascompared with other existing semiconductor materials such as Si and GaAsas described above.

DISCLOSURE OF INVENTION

The invention has been conducted in view of the abovementionedcircumstances of the prior art. It is an object of the invention toprovide single crystal SiC in which the crystal orientation can beeasily specified, and which is large and has a very high quality, and amethod of producing single crystal SiC in which the growing rate ofsingle crystal SiC is made higher so that a single crystal having a highquality can be produced with a high productivity.

The single crystal SiC of the first invention is characterized in that acomplex in which plural plate-like single crystal SiC pieces are stackedwhile crystal orientation faces of the SiC pieces are arranged in asubstantially same plane and crystal orientations are unified into onedirection, and a polycrystalline plate consisting of Si and C atoms isstacked on the crystal orientation faces of the plural stacked singlecrystal SiC pieces is subjected to a heat treatment, whereby a singlecrystal is grown from the crystal orientation faces of the plural singlecrystal SiC pieces toward the polycrystalline plate.

The method of producing single crystal SiC of the second invention ischaracterized in that plural plate-like single crystal SiC pieces arestacked while crystal orientation faces of the SiC pieces are arrangedin a substantially same plane and crystal orientations are unified intoone direction, and then secured by a sintered carbon jig, apolycrystalline plate consisting of Si and C atoms is stacked on thecrystal orientation faces of the plural single crystal SiC pieces whichare secured in a stacked state, and the complex is then subjected to aheat treatment, whereby a single crystal is grown from the crystalorientation faces of the plural single crystal SiC pieces toward thepolycrystalline plate.

According to the thus configured first and second inventions, theproperty that, when plural plate-like single crystal SiC pieces are usedin a stacked state, the crystal orientations of the plural singlecrystal SiC pieces are easily unified into one direction is effectivelyused, a polycrystalline plate consisting of Si and C atoms is stacked onthe specified crystal orientation faces, and a heat treatment isthereafter conducted, with the result that all polycrystals of thepolycrystalline plate are oriented by phase transformation in the samedirection with respect to the crystal axes of the plural single crystalSiC pieces, thereby enabling the single crystals which are grown at ahigh speed toward the polycrystalline plate to be integrated. Therefore,high-quality single crystal SiC in which crystalline nuclei, impurities,micropipe defects, and the like are not generated in an interface, andwhich is thick can be efficiently grown. Thus, it is possible to attainan effect of expediting the practical use of single crystal SiC which issuperior in high-temperature properties, high-frequency properties,dielectric strength, resistance to environments, and the like toexisting semiconductor materials such as Si (silicon) and GaAs (galliumarsenide), and which is expected as a semiconductor material for a powerdevice.

In the single crystal SiC of the first invention and the method ofproducing single crystal SiC of the second invention, when the crystalorientation faces of the plural single crystal SiC pieces for formingthe complex are adjusted by a grinding or polishing process so as tohave a surface roughness which is smaller than 1,000 angstroms RMS,particularly, in the range of 100 to 500 angstroms RMS, crystallinenuclei are sufficiently suppressed from being generated in the interfacewhile the crystal orientation faces of the plural single crystal SiCpieces on which the polycrystalline plate is to be stacked can be easilyprocessed into faces in which physical unevenness is small, therebyattaining an effect that the quality of single crystal SiC can beimproved.

In the single crystal SiC of the first invention and the method ofproducing single crystal SiC of the second invention, when thepolycrystalline plate for forming the complex is grown by the thermalchemical vapor deposition method and then polished so as to have athickness of 300 to 700 μm, particularly, about 500 μm, a mismatch of acrystal lattice caused by lattice distortion of the crystal orientationfaces of the plural single crystal SiC pieces can be eliminated by aheat treatment for a short time period, thereby attaining an effect thatsingle crystal SiC having a high quality can be produced with a highproductivity.

In the method of producing single crystal SiC of the second invention,under a state where the complex is accommodated in a carbon containerand the outer side of the carbon container is surrounded and coveredwith SiC powder, the heat treatment of the complex may be performed at atemperature in a range of 1,850 to 2,400° C. In this configuration, whenthe polycrystalline plate is a polycrystalline β-SiC plate which isgrown by the thermal chemical vapor deposition method, particularly, theheat treatment may be performed at a temperature in a range of 1,850 to2,400° C. under a state where the surface of the β-SiC polycrystallineplate is polished, carbon is placed on the polished surface of thepolycrystalline β-SiC plate, the complex is then accommodated in thecarbon container, and the outer side of the carbon container issurrounded and covered with SiC powder. According to this configuration,the SiC powder which is placed in the high-temperature atmosphere duringthe heat treatment is decomposed, and at least part of decomposed Si andC is moved into the container through the carbon container, so that theheat treatment can be performed in a saturated SiC vapor atmosphere.Accordingly, degradation of the quality due to the decomposition of thesingle crystal SiC pieces and the polycrystalline plate can besuppressed, thereby attaining an effect that it is possible to surelyproduce single crystal SiC of a higher quality.

In the method of producing single crystal SiC of the third invention,the surface of the single crystal SiC which is produced by theproduction method of the second invention is again ground or polished, apolycrystalline plate is then stacked on the ground or polished surfaceof the single crystal SiC, and the complex is thereafter subjected to aheat treatment, whereby a single crystal is grown from a crystalorientation face of the single crystal SiC toward the polycrystallineplate.

According to the thus configured third invention, an effect is attainedthat single crystal SiC which has a high quality and also a very largethickness and which has wide applicability as a semiconductor materialcan be easily obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic perspective view showing a single crystal α-SiCingot which is used as a raw material of plate-like single crystal α-SiCpieces to be used in the method of producing single crystal SiCaccording to the invention, and which is produced by the Achison method,

FIG. 2 is a front view of a plate-like single crystal α-SiC piece whichis cut out from the single crystal α-SiC ingot,

FIG. 3 is a side view of the plate-like single crystal α-SiC piece,

FIG. 4 is a front view of a single crystal α-SiC piece which is cut outfrom the plate-like single crystal α-SiC piece and in which the size isadjusted,

FIG. 5 is a side view of the single crystal α-SiC piece,

FIG. 6 is a schematic perspective view showing a state where a pluralityof the single crystal α-SiC pieces are secured in a stacked and closelycontacted state,

FIG. 7 is a schematic side view showing a state where a polycrystallineβ-SiC plate is grown by the thermal chemical vapor deposition method oncrystal orientation faces of the plural single crystal α-SiC pieceswhich are stacked and closely contacted,

FIG. 8 is a schematic side view showing a heat treatment state of acomplex, and

FIG. 9 is an enlarged side view of main portions and showing a statewhere single crystal SiC is grown by a heat treatment.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment will be described. FIGS. 1 to 9 sequentiallyillustrate production steps of the method of producing single crystalSiC according to the invention. In FIG. 1, 1 denotes a single crystalhexagonal α-SiC ingot (6H type or 4H type) which is produced by theAchison method. As shown by the arrow in FIG. 1, the single crystalα-SiC ingot 1 has many plate-like single crystal SiC pieces 1A of a widevariety of sizes, and is provided with a feature that the crystalorientation can be easily specified.

As shown in FIGS. 2 and 3, thereafter, many plate-like single crystalSiC pieces 1A are cut out from the single crystal α-SiC ingot 1. Asshown in FIGS. 4 and 5, from the plate-like single crystal SiC pieces1A, rectangular plate-like single crystal α-SiC pieces 2 in which thelength L of one edge is about 1 cm and the thickness T is about 0.5 mmare then cut out along the (110) crystal orientation faces 2a, and thecrystal orientation faces 2a are polished so that the pieces areadjusted so as to have the same size.

As shown in FIG. 6, thereafter, a plurality, for example, about 20pieces of the single crystal α-SiC pieces 2 which are adjusted in sizeas described above are secured to a sintered carbon jig 3 while they arearranged with setting their crystal orientation faces 2a to be in asubstantially same plane and the faces of the C-axis direction, i.e.,(0001) faces are stacked and closely contacted with one another so thatthe crystal orientations are unified into one direction. The crystalorientation faces 2a of the plural single crystal α-SiC pieces 2 whichare secured to the sintered carbon jig 3 are subjected to a grinding orpolishing process so that physical unevenness is eliminated.

More specifically, the crystal orientation faces 2a are adjusted so asto have a surface roughness which is smaller than 1,000 angstroms RMS,preferably, in the range of 100 to 500 angstroms RMS.

As shown in FIG. 7, thereafter, a β-SiC plate 4 is formed on the crystalorientation faces 2a of the plural single crystal α-SiC pieces 2 whichare stacked and closely contacted with one another, by the thermalchemical vapor deposition method (hereinafter, referred to as thethermal CVD method). After the growth by the thermal CVD method, thesurface of the β-SiC plate 4 is polished so that the thickness t becomes300 to 700 μm, preferably, about 500 μm.

Next, carbon 5 is placed on the polished surface of the β-SiC plate 4 ofa complex M consisting of the plural single crystal α-SiC pieces 2 andthe β-SiC plate 4. As shown in FIG. 8, thereafter, under a state wherethe complex M is accommodated in a carbon container 6 and the outer sideof the carbon container 6 is surrounded and covered with α-SiC powder 7,the complex is heat-treated while it is held for about 20 hours at atemperature of 1,850 to 2,400° C., preferably, 2,200° C. As a result, asshown in FIG. 9, single crystal α-SiC 2' which is oriented in the samedirection as the crystal axes of the single crystal α-SiC pieces 2 isintegrally grown from each of the crystal orientation faces 2a of thesingle crystal α-SiC pieces 2 toward the β-SiC plate 4.

The single crystal SiC which was produced by the above-describedproduction steps was cooled, and the surface of the single crystal wasthen polished and etched by molten potassium hydroxide (KOH). Thesurface was then magnified and observed under a Nomarski microscope,with the result that no grain boundary was found and etch pits in thesame direction as a hexagon were seen. From this, it was noted thatsingle crystal α-SiC was grown.

As described above, when the plural single crystal α-SiC pieces 2 whichare cut out into a rectangular plate like shape from the single crystalα-SiC ingot 1 produced by the Achison method are used in a stacked andclosely contacted state, the crystal orientations of the plural singlecrystal α-SiC pieces 2 can be easily specified into one direction. Whenthe complex M which is configured by forming the β-SiC plate 4 on thespecified crystal orientation faces 2a is heat-treated, the singlecrystals 2' all of which are grown at a high speed toward the β-SiCplate 4 with being oriented in the same direction with respect to thecrystal axes of the plural single crystal SiC pieces 2 can be integratedby recrystallization of polycrystals of the β-SiC plate 4. According tothis configuration, high-quality single crystal SiC in which crystallinenuclei, impurities, micropipe defects, and the like are not generated inan interface, and which is thick can be efficiently produced.

Particularly, it is preferable to adjust the crystal orientation faces2a of the plural single crystal α-SiC pieces 2 by a grinding orpolishing process so as to have a surface roughness which is smallerthan 1,000 angstroms RMS, preferably, in the range of 100 to 500angstroms RMS. The employment of the adjustment of the surface roughnessenables high-quality single crystal SiC in which a mismatch of a crystallattice is eliminated and crystalline nuclei and the like are notgenerated in an interface, to be obtained although less process labor isconsumed. Namely, physical unevenness of the crystal orientation faces2a of the single crystal α-SiC pieces 2 on which the β-SiC plate 4 isgrown by the thermal CVD method is preferably as small as possiblebecause crystalline nuclei are less generated. However, a process ofattaining a surface roughness which is smaller than 100 angstroms RMSrequires much labor and a long time period. When the surface becomesrough or the surface roughness exceeds 1,000 angstroms RMS, phasetransformation occurs simultaneously from a bottom face and a side faceof a concave portion in a heat treatment. Therefore, the possibility ofeliminating a mismatch of a crystal lattice is lowered, resulting in alow-quality product in which crystalline nuclei are generated in aninterface.

Preferably, the β-SiC plate 4 is polished so that the thickness t aftergrowth is 300 to 700 μm, more preferably, about 500 μm. When the plateis polished after growth in this way, a mismatch of a crystal latticecaused by lattice distortion can be eliminated by a heat treatment for arelatively short time period, and the productivity of single crystal SiCof a higher quality can be improved. This will be described below. Whenthe β-Sic plate 4 is a thick film which is thicker than 700 μm, phasetransformation occurs during a heat treatment while lattice distortionof the original crystal is maintained. In order to eliminate latticedistortion, therefore, a heat treatment for a long term is required,thereby producing a fear that the productivity of single crystal SiC ofa higher quality is lowered. A mismatch of a crystal lattice caused bylattice distortion in the crystal orientation faces 2a of the pluralsingle crystal α-SiC pieces 2 which serve as the foundation of the β-SiCplate 4 tends to be suddenly eliminated in the range of about 300 to 700μm of the thickness from the single crystal α-SiC pieces. When thethickness exceeds 700 μm, the degree of elimination of a mismatch of acrystal lattice is reduced.

In the heat treatment of the complex M, the surface of the β-Sic plate 4after the growth is polished, the carbon 5 is placed on the polishedsurface, under a state where the complex M is accommodated in the carboncontainer 6 and the outer side of the carbon container 6 is surroundedand covered with the α-SiC powder 7, the complex is subjected to apredetermined heat treatment. According to this configuration, the α-SiCpowder 7 is decomposed in a high-temperature atmosphere, and at leastpart of decomposed Si and C is moved into the container 6 through theporous carbon container 6, so that the predetermined heat treatment canbe performed in a saturated SiC vapor atmosphere. Accordingly, thedecomposition of the single crystal α-SiC pieces 2 and the β-SiC plate 4can be suppressed, whereby single crystal SiC of a high quality can beproduced and Si and C which are moved into the container 6 through theporous carbon container 6 are prevented from adhering to SiC beforephase transformation. As a result, it is possible to produce singlecrystal SiC which has a high quality and is beautiful.

When steps of again grinding or polishing the surface of the singlecrystal SiC which is produced as a result of the above-mentioned steps,and forming the β-Sic plate 4 on the polished surface by the thermal CVDmethod, and the heat treatment of the complex M including the β-SiCplate 4 are repeated, it is possible to obtain single crystal SiC havinga large thickness along the crystal orientation. When stacked singlecrystal α-SiC pieces 2 are juxtaposed, the β-SiC plate 4 is formed onthe whole area of the crystal orientation faces 2a of the group of thejuxtaposed stacked single crystal α-SiC pieces 2 by the thermal CVDmethod, and the abovementioned heat treatment is then conducted, it ispossible to obtain single crystal SiC which is large also in the term ofarea.

In the embodiment, the plate-like single crystal α-SiC pieces 2 are usedas the single crystal SiC pieces. Alternatively, for example, plate-likecrystal pieces such as α-SiC sintered members or single crystal β-SiCmembers may be used. In the embodiment, the crystalline β-SiC plate 2which is grown on the crystal orientation faces 2a of the plural singlecrystal α-SiC pieces 2 by the thermal CVD is used as the polycrystallineplate. Alternatively, for example, a polycrystalline α-SiC plate, an SiCsintered member of high purity, or an amorphous plate of high purity(10^(14atm) /cm³) or less may be used, and it is possible to obtainsingle crystal SiC of a high quality in the same manner as theembodiment.

As the single crystal α-SiC pieces 2 in the embodiment, either of the 6Htype or the 4H type may be used. When the 6H type is used, a singlecrystal which is converted from polycrystals of the polycrystallineβ-SiC plate 2 into α-SiC as the progress of the heat treatment is easilygrown in the same form as that of a single crystal of the 6H type. Whensingle crystal pieces of the 4H type are used, a single crystal in thesame form as that of a single crystal of the 4H type is easily convertedand grown.

INDUSTRIAL APPLICABILITY

As described above, the invention is a technique that a complex in whicha polycrystalline plate consisting of Si and C atoms is stacked oncrystal orientation faces of plural plate-like single crystal SiC piecesthat are stacked and closely contacted while crystal orientations areunified into one direction is subjected to heat treatment, so that asingle crystal which is oriented in the same direction as the crystalaxes of the single crystal pieces is integrally grown from the crystalorientation faces of the single crystal SiC pieces toward thepolycrystalline plate, whereby high-quality single crystal SiC in whichcrystalline nuclei, impurities, micropipe defects, and the like are notgenerated in an interface, and which is thick can be efficientlyproduced.

What is claimed is:
 1. Single crystal SiC characterized in that acomplex in which plural plate-like single crystal SiC pieces are stackedwhile crystal orientation faces of said SiC pieces are arranged in asubstantially same plane and crystal orientations are unified into onedirection, and a polycrystalline plate consisting of Si and C atoms isstacked on the crystal orientation faces of said plural stacked singlecrystal SiC pieces is subjected to a heat treatment, whereby a singlecrystal is grown from the crystal orientation faces of said pluralsingle crystal SiC pieces toward said polycrystalline plate.
 2. Singlecrystal SiC according to claim 1, wherein said plural single crystal SiCpieces for forming said complex are single crystal α-SiC.
 3. Singlecrystal SiC according to claim 1, wherein said polycrystalline plate forforming said complex is a polycrystalline β-SiC plate which is grown bya thermochemical vapor deposition method on the crystal orientationfaces of said plural single crystal SiC pieces, the crystal orientationfaces being arranged in a substantially same plane.
 4. Single crystalSiC according to claim 1, wherein the crystal orientation faces of saidplural single crystal SiC pieces for forming said complex are adjustedby a grinding or polishing process so as to have a surface roughnesswhich is smaller than 1,000 angstroms RMS.
 5. Single crystal SiCaccording to claim 4, wherein the crystal orientation faces of saidplural single crystal SiC pieces for forming said complex are adjustedby a grinding or polishing process so as to have a surface roughness ina range of 100 to 500 angstroms RMS.
 6. Single crystal Sic according toclaim 3, wherein a Surface of said polycrystalline β-SiC plate which isgrown by the thermochemical vapor deposition method is polished so as tohave a thickness of 300 to 700 μm.
 7. Single crystal SiC according toclaim 6, wherein the surface of said polycrystalline β-Sic plate whichis grown by the thermochemical vapor deposition method is polished so asto have a thickness of about 500 μm.
 8. A method of producing singlecrystal SiC characterized in that plural plate-like single crystal SiCpieces are stacked while crystal orientation faces of said singlecrystal SiC pieces are arranged in a substantially same plane andcrystal orientations are unified into one direction, and then secured bya sintered carbon jig, a polycrystalline plate consisting of Si and Catoms is stacked on the crystal orientation faces of said plural singlecrystal SiC pieces which are secured in a stacked state, andsaid complexis then subjected to a heat treatment, whereby a single crystal is grownfrom the crystal orientation faces of said plural single crystal SiCpieces toward said polycrystalline plate.
 9. A method of producingsingle crystal SiC according to claim 8, wherein single crystal α-SiC isused as said plural single crystal SiC pieces for forming said complex.10. A method of producing single crystal SiC according to claim 8,wherein a polycrystalline β-SiC plate which is grown by a thermochemicalvapor deposition method on the crystal orientation faces of said pluralsingle crystal SiC pieces is used as said polycrystalline plate forforming said complex, the crystal orientation faces being arranged in asubstantially same plane.
 11. A method of producing single crystal SiCaccording to claim 8, wherein the crystal orientation faces of saidplural single crystal SiC pieces for forming said complex are adjustedby a grinding or polishing process so as to have a surface roughnesswhich is smaller than 1,000 angstroms RMS.
 12. A method of producingsingle crystal SiC according to claim 11, wherein the crystalorientation faces of said plural single crystal SiC pieces for formingsaid complex are adjusted by a grinding or polishing process so as tohave a surface roughness in a range of 100 to 500 angstroms RMS.
 13. Amethod of producing single crystal SiC according to claim 10, wherein asurface of said polycrystalline β-SiC plate which is grown by thethermochemical vapor deposition method is polished so as to have athickness of 300 to 700 μm.
 14. A method of producing single crystal SiCaccording to claim 13, wherein the surface of said polycrystalline β-SiCplate which is grown by the thermochemical vapor deposition method ispolished so as to have a thickness of about 500 μm.
 15. A method ofproducing single crystal SiC according to claim 9, wherein singlecrystal α-SiC pieces which are cut out in a plate-like shape from asingle crystal α-SiC ingot along a crystal orientation face and whichare adjusted so as to have the same size are used as said plural singlecrystal SiC pieces for forming said complex.
 16. A method of producingsingle crystal SiC according to claim 8, wherein the heat treatment ofsaid complex is performed at a temperature in a range of 1,850 to 2,400°C. under a state where said complex is accommodated in a carboncontainer, and an outer side of said carbon container is surrounded andcovered with SiC powder.
 17. A method of producing single crystal SiCaccording to claim 10, wherein the heat treatment of said complex isperformed at a temperature in a range of 1,850 to 2,400° C. under astate where a surface of said β-SiC polycrystalline plate which is grownby the thermochemical vapor deposition method is polished, carbon isplaced on the polished surface of said polycrystalline β-SiC plate, saidcomplex is then accommodated in a carbon container, and an outer side ofsaid carbon container is surrounded and covered with SiC powder.
 18. Amethod of producing single crystal SiC wherein, after the surface ofsaid single crystal SiC which is produced by the method according toclaim 8 is again ground or polished,a polycrystalline plate is stackedon the ground or polished surface of said single crystal SiC, and saidcomplex is thereafter subjected to a heat treatment, whereby a singlecrystal is grown from a crystal orientation face of said single crystalSiC toward said polycrystalline plate.